I agree with most of what D-Tum has to say. Good sensible stuff. You can't say it too often -- cats think like cats much of the time, although they do adopt thought patterns from other species when they are constantly in contact.
But I think I know exactly what is wrong with your cat, because I have had two cats in similar moods. One was the classic newcat problem -- I adopted (or rather my dog did) a female kitten after my 3-year old male, Happy, had gotten used to sharing the house only with me and the dog. Happy went ballistic, and, being really dumb about cats, I tried to punish him, throw him out of the house, chase him with a broom, and otherwise treat him like an irrational criminal. I did everything wrong, and to the end of his days (8 more years actually), he growled around the house and made us all miserable. When he was crushed to death in the jaws of two playful neighborhood labradors, I could see the female cat (Gypsy) give a sigh of relief. And for a few years, she was the only cat. Then I inadvertantly destroyed her calm by adopting the first of many, many kittens and strays. For 4 long years, she attacked me, scratched when I tried to pet her, spat at me, growled, decided she want to sleep on a very high bookcase, and sometimes jumped down like a bomb to deliberately try to hit me or any of the other cats. Several times she even made my bed into her litter box -- a final insult and territorial statement. If I had not loved her so much, and if I had not learned anything from the earlier experience with my first cat, I think I would have had her put to sleep. You could not walk anywhere near her without getting your ankles scratched. I started to keep night lights on in case I inadvertantly ran into her in the dark. She fought with all the other cats. But she didn't move out. She seemed to take a sour pleasure in making everyone tiptoe around her.
I said this went on 4 years. Meanwhile, thanks to observing more and more cats, I took a different tack. I never tried to touch her, but I talked to her soothingly every chance we met or when I was putting her food dish down. Sometimes she would look at me and I could see how hurt she felt, but I didn't try to pet her. The few times I broke down, she leaned her head into my hand and then suddenly seemed to remember that I had destroyed her joy in life and she would lash out.
Around the beginning of the 5th year (last year), she began to sit nearer to me when I was working, or I would wake up in the morning and find she had come onto the bed and curled up by my pillow. This was a little scary, but I didn't try to throw her off and I resolutely turned my face away from her favorite nesting place every night. One night another cat came in and disturbed her and one of them, in the brief fight, clawed my face badly. Panic. But I tried to rearrange the bed in relation to the window (where the cats come in) and kept on tolerating her sleeping by the pillow. Sometime in the winter I started to occasionally give her a brief, and gentle, pat on the head. She accepted this, but growled when I tried to touch her neck or back. I have now worked my way down her back to within about 3 inches of her tail. She still does not tolerate my petting her below that, and she does not want me to touch her legs -- and I am not fool enough to touch her on the belly. She rarely lashes out at me when I am passing her, and never lately uses her claws in any case. If I have petted her enough, she puts one claws-out foot against my hand and then withdraws it.
Enough, she says in her clear body language, I am still hurt by your betrayal with all these cats and now dogs. I'm not ready yet to forgive or forget.
She rarely fights with the other cats now, although she occasionally swipes at a newcat. They learn quickly to avoid her. In fact I learned how to deal with her by watching them. She is getting old now, and I don't know if we will ever reconcile completely, but she is more at ease these days and more relaxed with all the other members of the household.
It is a cliche to speak of jealousy and cats, but it is no joke at all. Those cats that are reared in a multi-cat household recognize that everyone has their own territorial spac and the right to walk around without being attacked. But a cat who has been a single for a while is like a single child with the sudden arrival of a new baby. And sometimes the jealousy can be deadly, as in my Gypsy's case.
So consider not trying to touch your cat, but only talk to him. If you have to pick him up (if he will accept that), then put one hand on the nap of his neck in the classic pick-up hold -- not roughly, but just enough to ensure that he will not suddenly get away with twisting and clawing you. Walk around him. It is only prudent, and permits the cat to feel safe and isolated in his own territorial space. Above all, talk to him as you would a brain-damage child. Sweet, dulcet tones, soothing whispers, gentle sing-songs.
Don't blame the cat and don't you blame your sister (or she, you). Collaborate never to enter the reach of the cat except to feed and talk, and if he lets you, a very brief touch or petting, hand withdrawn slowly, all the time talking baby-talk for you, and hopefully more caressing from your sister, who is his surrogate mother. One last note -- you should both be giving extra attention to your own cats at such a time, and perhaps gradually introduce all of them to mutual pay together (rolling balls, dangly things on sticks...), taking care that the games become interactive instead of your cats and gainst the newcomers... And find separate places for the cats to sleep away from each other. It will give them a sense of safety.
Above all this, patience, patience, patience.
See if it doesn't help.